Whenever you developing the new theme. You need to add following code in your theme file.
wp_head
Goes in the HTML <head> element of a theme; header.php template. Example plugin use: add javascript code.
Usage: <?php do_action('wp_head'); ?>
-or- <?php wp_head(); ?>
wp_footer
Goes in the “footer” of a theme; footer.php template. Example plugin use: insert PHP code that needs to run after everything else, at the bottom of the footer.
Usage: <?php do_action('wp_footer'); ?>
-or- <?php wp_footer(); ?>
wp_meta
Typically goes in the <li>Meta</li> section of a theme’s menu or sidebar; sidebar.php template. Example plugin use: include a rotating advertisement or a tag cloud.
Usage: <?php do_action('wp_meta'); ?>
-or- <?php wp_meta(); ?>
comment_form
Goes in comments.php and comments-popup.php, directly before the comment form’s closing tag (</form>). Example plugin use: display a comment preview.
Usage: <?php do_action('comment_form', $post->ID); ?>
Note: don’t forget to add wp_head, wp-footer and wp_meta methods in you theme.
wordpress filter and hooks are always important for wordpress theme and plugins development.